Non-electric initiating assembly



Feb. 25, 1964 R. J. MILLER 3,122,097

NON-ELECTRIC INITiATING ASSEMBLY Filed Oct. 10, 1961 FIG. F|G.2

INVENTOR ROSS JAY MILLER BY g A.

ATTORNEY United States Patent 3,122,097 NON-ELECTRIC INITIATlNG ASSEMBLYRoss Jay Miller, Pitrnan, NJ., assignor to E. I. du Pont de Nernours andCompany, Wilmington, Del., a corporation of Delaware Filed Get. 10,1961, Ser. No. 144,149 6 Claims. (Cl. 102-27) tained within a sheath ofa ductile metal which is sub-' sequently covered with one or more layersof reinforcing and/or waterproofing material. Due to its ability topropagate a detonation impulse without attendant brisance and because itis free from the hazards associated with electric initiators, in manyblasting operations this cord has replaced conventional detonating fuseand electrical initiators.

However the aforedescribed cord, owing to the low loading of explosivecontained in the core, does not initiate the explosive compositionsconventionally used in blasting. Consequently, auxiliary means areneeded to relay the detonation stimulus from the low-energy connectingcord to the explosive charges to be initiated. In cases where it isdesirable to provide a delay interval between initiation of the mainexplosive charges to permit the burden loosened by a proceeding blast toclear, to reduce ground vibration, and to improve fragmentation, a delayinitiator actuated by the connecting cords detonation can be used.

In accordance with this invention, there is provided a non-electricinitiating assembly comprising a tubular shell integrally closed at oneend, said shell housing, in sequence from said closed end, a base chargeof detonating explosive, a priming charge of a heat-sensitive detonatingexplosive, and a charge of an exothermic-burning composition, a tubularcapsule positioned within the said shell contiguous to said exothermicburning composition, said capsule having a closure at one end providedwith a central aperture therethrough, and a looped section of low-energyconnecting cord extending into the said shell, the lower looped portionof said cord being positioned adjacent to said capsule and in ignitingrelationship to said exothermic burning composition.

In a preferred embodiment of this invention, the looped section of thecord is of U-shaped configuration. In a particularly preferredembodiment of this invention, a perforation, e.g., a pin hole or slit isprovided in at least a portion of the countering of the looped sectionof the cord. In a still further embodiment of this invention, the loopedsection of cord is positioned in the shell by means fo a plug of aresilient composition which is in snug peripheral engagement with theinner walls of the rigid shell of the auxiliary initiator.

In order to describe the invention in greater detail, reference is madeto the accompanying drawings wherein:

FIGURE 1 is a cross-sectional drawing of an initiating assembly inaccordance with this invention and FIGURE 2 is a cross-sectional drawingof a modification of this invention adapted to give a delayed initiatingaction.

In FIGURE 1, 1 represents a tubular shell having one integrally closedend, 2 represents the connecting cord consisting of explosive core 3,metal sheath 4, and countering 5. The looped section 6 of the cord 2 isheld within a plug 7 which closes the open end of shell 1. Within shell1 are, in sequence, a base charge 8 of a detonating 3,122,097 PatentedFeb. 25, 1964 explosive, a priming charge 9 of a heat-sensitivedetonating explosive, an exothermic-burning composition 10, and aspacing means, i.e., an open-ended capsule 11, having a central aperture12. An air gap 13 is formed within the space enclosed by capsule 11.Peripheral crimps 14 hold the plug and cord 2 in place.

The assembly depicted in FIGURE 2 is identical to that of FIGURE 1except that a delay carrier 15 containing a delay composition 16 isinterposed between the primer 9 and the exothermic burning composition10.

In operation of the initiator, the initiation impulse propagated by thedetonation of the explosive cord is transmitted from the explosive corethrough the lead sheathing in the looped section of the cord, probablywith the formation of hot, minute missiles of the ductile metal, jumpsthe air gap 13 enclosed by the capsule 11, passes through aperture 12and ignites the exothermic burning delay composition 10. Thiscomposition burns at high temperature, and when the hot front reachesthe priming charge 9, the latter is ignited. The priming charge, inturn, initiates the base charge 8. The initiator of the design of FIGURE1 can be designed to provide a precise delay of from 1 to 1000milliseconds, the length of the delay period depending upon the depth ofthe exothermic burning composition, since the burning time of the exothermic burning charge is proportional to the depth of this charge. Alonger delay, e.g., l-ZO seconds, is provided by the assembly of FIGURE2 wherein the exothermic burning composition 10 ignites delaycomposition 16 in the delay carrier 15. This delay composition in turnignites the priming charge 9.

While it is not desired for this invention to be limited by theory, itis believed that the improved initiation characteristics provided by thelooped section of low-energy cord is due to increased confinement of theexplosive core of the lowenergy connecting cord so that adoublebarrelled initiation effect is achieved. That is, a portion of thedetonation impulse is propelled through the looped section directly inthe form of a front of hot lead particles, reaction products, and flame,while a remaining portion is transmitted through the folded back sectionof cord with the result that there is a propulsion of detonationproducts and flame through the looped section.

When low loadings of explosive are used in the core, i.e., less thanabout 1.0 grains per foot, or the countering on the cord is relativelythick, it is preferred to perforate the looped section so that the majorportion of the detonation impulse will be transmitted from the loopedsection of cord to the exothermic burning composition and not expendedin burning through the countering. The perforation which may be providedin the looped section of the cord may be a pinhole or slit, or an entiresection of the countering may be removed from the looped section of thecord either by cutting as with a knife or by otherwise stripping away asection of the countering. The sheathing of ductile metal should not becut. Rupture of this sheathing may result in loss of the explosive coreand subsequent cut-off of the detonation impulse.

The looped section 6 of the cord 2 may be formed simply by folding thecut end of the cord 2, to be inserted in initiator shell 1, back uponthe length of cord 2 at an angle of about to At angles less than about95 the double barrelled initiation effect is not achieved and housingproblems are encountered. At angles greater than about 180, the leadsheathing may be ruptured with subsequent loss of the explosive core.For low-energy connecting cord having an explosive loading of 0.5 to 2.0grains per foot, it has been determined that the length of the foldedback segment of cord should be at least about /4 inch, i.e., thedistance from the end of the cord to the vertex of the angle should beabout A inch. This folded-back segment insures that sulficient backwardpropulsion of detonation products will occur to initiate even veryinsensitive exothermic compositions over an air gap up to one inch. Thelooped section of cord also may be provided simply by tying a knot inthe end of the cord to be inserted into the initiator.

The air gap or distance between the lower portion of the looped sectionof cord and the exothermic burning composition may be regulated, e.g.,to focus the initiation impulse, by the provision of an appropriatespacing means which also acts to hold the exothermic burning compositionin position. This spacing means preferably is a capsule whose depth maybe varied and which is provided with a central aperture. The low-energyconnecting cord may be inserted in the device until it reaches thebottom of the capsule or may be spaced from the open end of the capsule,provided that the distance between the lowermost portion of the loopedcord to the delay composition does not exceed one inch. A separationgreater than one inch results in unreliable functioning of the device.Within this range, from contact up to one inch, however, exceptionallyreliable performance was obtained in testing the initiators. Obviously,the allowable variance is an asset in the use of initiators in the fieldsince this allows reliable initiation even though the cord should beinadvertently pulled or moved during the blasting operation.

It is preferred that the open-ended spacing capsule be positioned withthe open-end directed away from the loaded charges as the roundedcorners of the capsule thus inserted act as a retaining medium for theadjacent exothermic-burning composition. However, the capsule may bepositioned so that the open-end is directed toward the charges. Thedimensions and shape of the aperture in the capsule are not critical.The aperture is present in the capsule in order to facilitatetransmission of the initiation impulse from the detonation of theexplosive core of the connecting cord to the delay composition. As longas there is an opening in the capsule, this condition will be satisfied.

In order to illustrate specific embodiments of this invention, referenceis made to the following examples. These examples are to be understoodto be illustrative only and not limiting the invention in any way.

Example 1 Twenty initiators were prepared resembling that of FIGURE 1.In each case, the aluminum shell 1 1 inch in length, 0.278 inch inoutside diameter had a 0.010-inch wall thickness. As a base charge, 7.2grains of PETN was charged to each shell and compacted at 200 pounds bya pointed pin. Above this charge, 3.0 grains of lead azide, as theprimer, was loaded and compacted at 200 pounds by a fiat pin. Theexothermic-burning composition, 5.0 grains of a 1/99 mixture ofboron/red lead, grained with neoprene, was charged to each shell andcompacted at 200 pounds by a dimpled pin. An openended aluminum capsule,0.187 inch long and having a central aperture 0.080 inch in diameter wasinserted on top of the exothermic burning composition with the open enddirected away from the loaded charges. The end of a length of low-energyconnecting cord having 1 grain of lead azide per foot of lengthcontained in a split plug of polyethylene mating with the shell, wasturned back into the split to form a U-shaped loop wherein the lengthturned back section was /8 inch. A slit was made in the countering ofthis looped section of the cord. The plug containing the cord wasinserted into the assembled initiator until there was an air gap of 0.67inch between the looped cord and the exothermic burning composition.When fired, these units were initiated at low velocity, i.e., the lowenergy cord was actuated by a length of Primacord. All functionedproperly.

When an identical initiator was tested with a square-cut end of the lowenergy detonating cord, ignition of the exothermic burning compositionwas not effected.

4 Example 2 Delay initiators were assembled as in Example 1 except thatthe air gap between the base of the looped section of the cord and theexothermic burning composition, the explosive loading of the core, andthe length of the turned back section were varied.

A long-period delay initiator was assembled in an aluminumsheil havingessentially the same dimensions as the shell discussed in Example 1except that a longer length was required in order to accommodate thecharges. PETN and lead azide, as the base and priming charge, respectively, were loaded and compacted as in Exampie l. A delay carrierhaving a length of 1.063 inch and a shellwall thickness of 0.063 inchand containing a core of a 83/17 barium oxide/ selenium mixture, as aslow-burning delay composition, was placed adjacent to the primer. Ontop of the carrier 1 grain of the exothermic burning mixture of Example1 was loaded and pressed at 200 pounds by a fiat pin. The open-endedaluminum capsule was inserted as previously exemplified.

The looped end low-energy connecting cord containing 1 grain of leadazide per foot of length (/2 inch turnback) was inserted into thepolyethylene plug, and the plug and cord assembly inserted into theshell leaving an air gap of /s inch. Upon being fired, the initiatorgave a delay period of 5.4 seconds.

The plug used to position the looped section of the lowenergy connectingcord within the initiator shell may be formed of any material which isresilient, thermally stable, and of sufiicient structural strength tosecurely hold the cord within the shell under the conditions of use. Thedimensions of this plug naturally will depend upon the size of the shelland the physical properties of the material used. Exemplary of suitablematerials of construction for the plug are natural and synthetic rubbersand relatively long-chain polymers, e.g., polyethylene, polypropylene,neoprene, polyvinylidene chloride, polytet-rafiuoroethylene, and thelike.

The particular compositions used for the various charges are notcritical to the present invention, provided that the selectedcompositions function as desired. Accordingly, for the base charge, anyof the usual base changes may be used, e.g., RDX, lead azide, PETN,nitromannite, TNT, or HMX. As the priming charge, heat sensitivedetonating compositions such as lead azide, diazodinitrophenol, ormercury fnlminate may be used. Obviously when squib action is desired,the priming composition and the base charge may be identical. For theexothermic burning composition, an exothermic reacting mixture of ametal and an oxidizing agent of the type conventionally used in ventlessdelay initiators is preferred, e.g., boron-red lead, boron/redlead/dibasic lead phosphite, magnesium/barium/peroxide/selcnium, orsilicon/red lead. For long-period delay initiators, the delaycomposition within the delay carrier may be any of the conventional,gasless delay compositions which burn at a constant rate, such as amixture comprising barium peroxide and selenium; bismuth, selenium, andpotassium chlorate; lead and selenium; or magnesium and barium peroxide.The amount of each charge is varied depending upon the efiect desired.The composition of the rigid shell surrounding the changes or spacingthe charges is not critical; however lead or aluminum is preferred forease in handling and loading.

The base charge and priming charges may be compacted by various shapedpins, e.g., pointed, flat, conical or bell. Any compaction pressuresufiicient to retain the charges in the shell yet insufiicient to causedensitization of the charges is suitable.

The delay period is dependent upon the depth of the delay charge andamount of compaction of the exothermic burning composition. Accordingly,change in these variables will produce change in the delay period. Thelimits of pressure used to compact this charge are identical to thoseused for the base and priming charge, i.e., sufiicient to retain thecomposition in the shell without densitizing the charge. If desired, theexothermic-burning composition used may be grained prior to use forexample, with neoprene, gum, shellac, polyethylene glycol, Thiokol, andcarbowaxes. The graining facilities loading but is not critical to thefunctioning of the device.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is accordingly tobe understood that within the scope of the appended claims the inventionmay be practiced otherwise than specifically described.

What is claimed is:

1. A non-electric delay initiator comprising a tubular shell integrallyclosed at one end, said shell housing, in sequence from said closed end,a base charge of detonating explosive, a priming charge of aheat-sensitive detonating explosive and a charge of exothermic burningcomposition; a tubular spacer capsule positioned within the shellcontiguous to said exothermic burning composition, said capsule havingone closed extremity with a central aperture therethrough; and a sectionof low energy connecting cord extending into the shell, the lowerportion of said cord being looped and positioned adjacent to saidcapsule a distance of not greater than one inch from, and in ignitingrelationship to, said exothermic burning composition; said initiatorbeing adapted to provide a delay period of from :1 millisecond to 20seconds.

2, The initiator as claimed in claim 1, wherein the looped section ofsaid low-energy connecting cord is of U-shaped configuration.

3. The initiator as claimed in claim 1, wherein a plug of a resilientmaterial having an axial aperture there 6 through seals the openextremity of said shell, and wherein the looped section of low-energyconnecting cord passes through the axial aperture in said plug and isheld in initiating relationship to sai exothermic burning compositionthereby.

4. The initiator as claimed in claim 1, wherein a perforation isprovided in at least a portion of the countering of the lower loopedsection of the said cord.

5. The initiator as claimed in claim 1, wherein a delay carriercomprising a heavy-Walled tube of a rigid material containing a centralcore of a delay composition is interposed between said priming chargeand the exothermic-burning composition.

6.. A non-electric delay initiator comprising a metal tube integrallyclosed at one extremity, said tube housing in sequence from said closedextremity, a base charge of detonating explosive, a priming charge of aheat-sensitive detonating explosive and a charge of exothermic burningcomposition, a length of low energy connecting cord, extending into saidtube, said cord comprising a continuous core of a detonating explosiveat a loading of from 0.5 to 2 grains per foot encased in a sheath ofductile metal, the extremity of said cord Wtihin the tube being loopedin a U-shaped configuration and positioned to provide a distance ofgreater than Zero to one inch between said exothermic burningcomposition said loop, and a capsule having a closed extremity with acentral aperture therethrough positioned within said tube between saidloop and said exothermic burning composition, said capsule being adaptedto focus the initiation impulse which is propagated through thesheathing and countering of said cord at essentially the apex of saidloop, and to maintain the proper spacing between said loop and theexothermic burning composition.

References tlited in the file of this patent UNITED STATES PATENTS2,360,698 Lyte Oct. 17, 1944 2,400,103 Cobb May 14, 194-6 2,402,235Burrows et a1. June 18, 1946 2,558,134 Hall June 2-6, 1951 2,619,035Lewis et a1. Nov. 25, 1952 3,021,785 Hradel et al Feb. 20, 196 2 FOREIGNPATENTS 15,806 Germany Oct. 22, 1881 815,532 Great Britain June 24, 1959

1. A NON-ELECTRIC DELAY INITIATOR COMPRISING A TUBULAR SHELL INTEGRALLYCLOSED AT ONE END, SAID SHELL HOUSING, IN SEQUENCE FROM SAID CLOSED END,A BASE CHARGE OF DETONATING EXPLOSIVE, A PRIMING CHARGE OF AHEAT-SENSITIVE DETONATING EXPLOSIVE AND A CHARGE OF EXOTHERMIC BURNINGCOMPOSITION; A TUBULAR SPACER CAPSULE POSITIONED WITHIN THE SHELLCONTIGUOUS TO SAID EXOTHERMIC BURNING COMPOSITION, SAID CAPSULE HAVINGONE CLOSED EXTREMITY WITH A CENTRAL APERTURE THERETHROUGH; AND A SECTIONOF LOW ENERGY CONNECTING CORD EXTENDING INTO THE SHELL, THE LOWERPORTION OF SAID CORD BEING LOOPED AND POSITIONED ADJACENT TO SAIDCAPSULE A DISTANCE OF NOT GREATER THAN ONE INCH FROM, AND IN IGNITINGRELATIONSHIP TO, SAID EXOTHERMIC BURNING COMPOSITION; SAID INITIATORBEING ADAPTED TO PROVIDE A DELAY PERIOD FROM 1 MILLISECOND TO 20SECONDS.